1. Field of Invention
The invention relates to a method for setting a standard value by which banding is effectively obscured without significantly improving the mechanical precision of an ink jet printer and to an ink jet printer that is set up using the method.
2. Description of Related Art
Conventionally, there exist ink jet printers that form images on a recording medium using ink. In such ink jet printers, small dots are formed on the recording medium by selectively ejecting a small quantity of ink from a plurality of nozzles provided in an ink jet head, thereby forming the images on the recording medium. In such ink jet printers, the dots are formed on the recording medium, placed at a predetermined distance away from the nozzles, by ejecting ink droplets from the nozzles. Therefore, the dots tend to be displaced on the recording medium. More specifically, the ink droplets are not always ejected in a proper direction and at a right moment. Such displacements cause streaks, such as bands of discrete color or tone, in the images formed on the recording medium. The streaks, more particularly, unevenness in a sub-scanning direction produced by streaks extending in a main scanning direction, that is, banding, is one of big factors that leads to degraded images formed by the ink jet printer. It is considered that the elimination of banding is one of the most important requirements for securing high-quality images to be formed by the ink jet printer.
It is conceivable that position error of the nozzles provided in the ink jet head, a deviation of an ejecting direction of ink droplets from the nozzles, variations in an ink droplets ejecting speed, and a deviation of an average value of an amount of sheet feeding from an ideal value will cause the streaks. In order to obscure the banding produced by such causes, it is sufficient to improve the precision of the nozzles and the sheet feeding mechanism. However, in order to completely eliminate the banding, the nozzles and the sheet feeding mechanism have to be structured with extremely high precision, thereby significantly increasing the cost of the ink jet printer.